This invention relates generally to internal combustion engines and ignition systems thereof and more particularly to control of ignition timing of such engines. More specifically, the invention relates to an engine ignition timing control system which detects data such as the cam angle or the crank angle from a reference position in an engine and, in response, sets the ignition or firing timing.
In the prior art, in an ignition control system of the time-control type utilizing crank angle signals of even pitch, the accuracy of the reference position detection is improved by the measure of counting the angle signals with standard angle signals as reference thereby to increase the number of pulses, as set forth, for example, in Japanese Laid-Open Patent Publication No. 36961/1979. Furthermore, as disclosed in Japanese Laid-Open Patent Publication Nos. 183304/1984 and 61617/1985, a measure, for this purpose, of setting specific pulse positions at particularly narrow settings is proposed. Another measure proposed in Japanese Laid-Open Patent Publication No. 47877/1985 comprises removal of one specific pulse position.
In the method of the reference cited first above Japanese Laid-Open Patent Publication No. 36961/1979, however, in the case where the number of pulses is increased, it is necessary to carry out a measure for preventing misfiring, whereby the improvement in accuracy is not as much as would be expected from the increase in the number of pulses. Furthermore, the hardware for processing these pulses entails an increase in cost, and, if the processing of the pulses is imposed on the software in order to avoid this increase in cost, the interrupted overhead becomes large, whereby many parts of the main control are occupied by the program for processing the pulse.
Furthermore, the latter of the above references (Japanese Laid-Open Patent Publication Nos. 183304/1984, 61617/1985, and 47877/1985) merely teach the use of means for carrying out cylinder identification and provide no contribution whatsoever to improvement of precision of ignition timing.
An ignition timing control of the time control method is accompanied by the problem of great irregularities in the ignition timing at the time of starting of the engine.